1. Field of the Invention
This invention relates to an improved reactor with multistage stirrer elements and baffles and its use in the production of polysaccharide ethers, particularly cellulose ethers.
2. Statement of the Related Art
It is known that polysaccharide ethers, more especially cellulose ethers, can be produced by a multiple-step-reaction in which each step comprises alkalizing and then etherifying a suspension of finely divided cellulose, as described in U.S. Pat. No. 4,507,474 (and corresponding German application No. 33 03 153). The reactions preferably take place in stirred reactors, such as mixer-reactors, stirrer-equipped autoclaves, cascades or even in columns or screw reactors.
Such reactors are available in many different configurations, and commonly a particular reactor construction is suitable only for a particular set of reactants. Thus, a different reactor may be chosen depending upon whether carboxymethyl, methyl, hydroxyethyl, hydroxypropyl cellulose ethers or mixed ethers thereof are to be produced and also depending on the starting materials which, besides cellulose, may comprise starches and guar and also mixtures thereof and which may be used in various forms from powders to about 2 mm long fibers.
In addition to the fact that the particular reactor selected can only be used for certain starting materials and products, another disadvantage is that, in every case, the reaction is accompanied by relatively high external energy consumption. Thus, according to U.S. Pat. No. 4,063,018 for example, the reaction is carried out under wet grinding conditions whereas, according to British Pat. No. 1,253,726 (and corresponding published German application No. 19 11 993), the starting materials are vigorously mixed, preferably by a combined tumbling and beating movement. Alternatively, the necessary energy may be applied by pump recirculation through homogenizers, for example as described in U.S. Pat. No. 4,017,671 (and corresponding published German application No. 24 00 879).